The present invention relates to a plastic board, formed of injection-molded plastic, with an upper side, an underside and a peripheral edge surface. In addition, the present invention relates to a method for producing such a plastic board by an injection-molding technique.
The main application area for a plastic board according to the present invention is for the household and kitchen, food retailers and food production companies, where such plastic boards are used as cutting boards. Cutting boards of plastic have the great advantage that their surfaces have characteristics similar to wood surfaces in terms of their benign effect on knife blades, but can meet much higher requirements for hygiene in comparison. Cutting boards of plastic are accordingly in widespread use. They are usually produced from polypropylene or some other thermoplastic.
Plastic boards that are to be used in particular as cutting boards have a thickness of typically 8 to 10 mm, in order to ensure sufficient intrinsic stability when cutting food and the like. To allow a plastic product with such a wall thickness to be injection-molded, a disproportionately long cycle time is necessary.
In an injection-molding machine, plastic is plasticized and injected under pressure into an injection-molding tool. In the injection-molding tool, the plastic transitions back into the solid state again as a result of cooling down, and, after opening of the injection-molding tool, is removed as a finished part. Before the demolding, the plastic must however have solidified completely, in order to ensure dimensional accuracy of the finished part. In the case of thick-walled molds, this cooling process of course takes a disproportionately long time.
In the case of thick-walled sheet-like products, such as the plastic board in question, there is additionally the risk of warping after demolding, if the demolding takes place when the material has not cooled down sufficiently. Especially in the case of the preferred area of use as a cutting board, it is however of great importance that warping of the same is avoided. This is so because a cutting board must be absolutely flat in order for it not to wobble when it is being used.
In order to produce flat cutting boards in the necessary thickness of typically at least 8 mm by the injection-molding process, it is therefore necessary to leave the plastic that is forced into the injection-molding tool in the injection-molding tool for an extraordinary long time in order in particular for it to cool down substantially there before the finished product is demolded. In the case of cutting boards of polypropylene with a thickness of 8 mm that are demolded flat and not intended to warp, cycle times of typically approximately 6 minutes therefore result. By contrast, cycle times of injection-molded plastic household and kitchen containers are for example of the order of half a minute.
JP H10-243 884 A has disclosed a plastic board that is made up of two injection-molded halves. Both halves each have distributed over their surface area stabilizing elements that are arranged in an intermediate space between the two halves. The intermediate space is otherwise substantially unfilled. When the two halves are joined together, the stabilizing elements are placed one on top of the other and connected to one another in a material-bonded manner, in order as a result to fix the two halves to one another.
According to this reference, a method for producing a plastic board with an upper side, an underside and a peripheral edge surface by the injection-molding technique is carried out in such a way that a first half, which comprises at least the upper side of the plastic board, and a second half, which comprises at least the underside of the plastic board, are injection-molded. These two halves are then joined together, in order to form a plastic board with an upper side and an underside, the two halves being formed in such a way that at least one cavity forms between the halves when they are joined together. The two halves are fixed onto one another in order to complete the plastic board.
Accordingly, the plastic board according to the invention is formed substantially of an injection-molded first half, which comprises at least the upper side of the plastic board, and an injection-molded second half, which comprises at least the underside of the plastic board, the two halves being put together and fixed to one another. Between the two halves there is formed at least one cavity.
With these measures, the plastic board can be produced from two halves, the wall thicknesses of which are much smaller than the thickness of the finished plastic board. Accordingly, a very much shorter cycle time is required for the production of the two halves than when the plastic board is produced “in one piece” in a single injection-molding operation. Even if the required time for the joining together of the two halves of the plastic board according to the invention at the same time increases, a significantly shorter cycle time than was previously possible in the prior art is still obtained.
Then there is also the fact that the plastic board requires less material than a plastic board that is produced in a single injection-molding operation; this is so because the cavity, or possibly multiple cavities, form(s) a volume of the plastic board for which no plastic has to be used.